In order to precisely locate a medical device such as, for instance, a needle or catheter inside a patient, ultrasound imaging is commonly used. Ultrasound imaging relies on the different ways in which sound waves are reflected from interfaces between substances. Ultrasound waves, with frequencies above the audible range of normal human hearing, typically from 20 kHz up to several gigahertz, are reflected in areas of density differences. In practice, a transducer is used that emits ultrasound waves, where after some of the reflected sound waves are detected by the transducer, which turns the vibrations into electrical pulses. These electrical pulses are processed and transformed into digital images.
The use of ultrasound imaging for medical devices is well known in the art. In order to enhance the quality of ultrasound images of medical devices, the surface of such a device is typically grooved or otherwise roughened, or an ultrasound coating is applied to at least part of the surface of the device. For instance, U.S. Pat. Nos. 5,289,831 and 5,081,997 describe echogenic medical devices having a surface with partially spherical indentations, or having a surface that is coated with spherically shaped particles, which scatter an ultrasound signal. International Patent Application WO 00/51136 describes the use of gas bubbles or metal particles for enhancing an ultrasound signal. The use of an echogenic material containing cavities or gas bubbles is also described in European Patent Application Serial No. EP 0624342, whereas International Patent Publications WO 98/18387 and WO 00/66004 describe medical instruments with bubble-generating means, which produce bubbles that are visible with ultrasound. Additionally, U.S. Patent Publication 2004/0077948 discloses an echogenic surface having structures entrapping gas, the entrapped gas causing the device to be ultrasonically visible.
U.S. Patent Publication 2005/0074406 describes an ultrasound coating containing membranes encapsulating a gas-filled core.
European Patent Application Serial No. EP 1118337 and U.S. Pat. No. 6,506,156 use an echogenic layer including a polymeric matrix with a plurality of void spaces, or glass microsphere particles, or both. U.S. Patent Publication 2009/0318746 describes lubricious echogenic coatings containing polymeric gas-/liquid-containing microparticles.
The use of roughened surfaces in order to enhance ultrasound visibility, however, involves an increased risk of discomfort for the patient since a roughened surface typically requires more force to move the device inside the patient's body and gives only a limited ultrasound visibility enhancement. The use of gas bubbles for improving ultrasound visibility has the disadvantage that it is difficult to control the concentration and size of the formed bubbles, leading to variations between coatings so that it is more difficult to obtain an optimized ultrasound imaging coating.
The use of echogenic particles is, therefore, preferred. Although various alternatives for ultrasound imaging with microparticles are available, it is advantageous to optimize the visibility (i.e., the accuracy) of the obtained ultrasound images. It is an object of this disclosure to provide such optimized coatings for ultrasound detection.